One exemplary apparatus for producing a core yarn having a core fiber provided in a fiber bundle is a core yarn production apparatus as in Patent Document 1. In this production apparatus, a spinning device produces a core yarn by spinning using a core fiber, which is an elastic yarn supplied from a core fiber supply device, and covering fibers, which consist of a fiber bundle drafted by a drafting device. The core fiber supply device is provided with a core fiber detection sensor for detecting the core fiber, and when the sensor detects the absence of the core fiber, the spinning operation is stopped.
In the above-described core yarn production apparatus, however, the spinning might be carried out without placing the core fiber in the covering fibers, even when the core fiber detection sensor detects the core fiber. For example, when core yarns are spliced together, the core fiber might be suctioned into a suction nozzle after passing by an air spinning device, so that a yarn composed only of the covering fibers is spun by the spinning device. As a result, the yarn without a core fiber is wound into a package.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-363834 (elastic core fiber detection sensor 32 in FIG. 4, and paragraph 0058)